ADC predicts persistent cervical lymph node disease following curative (chemo)radiotherapy

Abstract

Purpose or Objective The value of diffusion weighted (DW)-MRI post (chemo)radiotherapy ((C)RT) to assess disease response in malignant cervical lymph nodes (LN) is incompletely understood. We assess the correlation between apparent diffusion coefficient (ADC) of cervical LN post (C)RT and subsequent neck dissection histopathology. Materials and Methods Patients treated with (C)RT for head and neck squamous cell carcinoma at a single institution with post-treatment MRI followed by surgical neck dissection from January 2017 - January 2020 were identified for this retrospective study. MRI scans were acquired at 1.5 T or 3 T on one of three scanners (Siemens Aera, Siemens Skyra, and GE Signa), and included structural sequences and DW-MRI with automatically generated ADC maps. The DW-MRI sequence parameters were comparable on all three scanners (b-values = 50 and 800 s/mm²). However, due to the limited field of view of the sequence, and the prioritisation of imaging primary disease, some of the DW-MRI scans did not include the full extent of neck nodes. Two experienced readers drew regions of interest (ROI) on the ADC maps over all identifiable cervical LN with a diameter greater than 5 mm, blinded to histopathological diagnoses, using the picture archiving and communication system (PACS). Mean and minimum ADC values (ADCmean and ADCmin) of each node were measured on the PACS workstation (by assessing the ADC of all pixels within the ROI) and matched to histopathological findings following neck dissection. An un-paired t-test was used to compare ADC values for benign and malignant cervical lymph nodes, with P < 0.05 considered statistically significant. Threshold ADC values for the detection of cervical LN malignancies were calculated using receiver operating characteristic (ROC) analysis. Results 31 cervical LN were identified in 18 patients. However, the ADCmin for two of the LN was 0 mm²/s, which may imply a failure in the ADC estimation, hence those two LN were excluded from analysis. For the remaining 29 nodes (14 malignant and 15 benign as confirmed on histology), there was no statistically significant difference between ADCmean for malignant (1.17 ± 0.36 x 10¯³ mm²/s) vs. benign (1.40 ± 0.53 x 10¯³ mm²/s) nodes (p = 0.18). A statistically significant difference was seen between ADCmin for malignant (0.42 ± 0.30 x 10¯³ mm²/s) vs. benign (0.72 ± 0.37 x 10¯³ mm²/s) nodes (p = 0.02). The ROC analysis indicated that an ADCmean threshold < 1.49 x 10¯³ mm²/s detected disease with 86% sensitivity, 33% specificity, and 59% accuracy. Whilst an ADCmin threshold < 0.69 x 10¯³ mm²/s had 86% sensitivity, 60% specificity, and 72% accuracy Conclusion ADCmin shows value in predicting persistent lymph node malignancy post-(C)RT in primary head and neck cancer and appears more discriminatory than ADCmean. Further prospective studies in a larger sample size are warranted.